Measuring Parameters for Microlensing Planetary Systems. Scott Gaudi Matthew Penny (OSU)

WFIRST Microlensing Survey.

Microlensing Survey Dataset. Properties. ~3 sq. deg. ~432 days. ~80% of the area will have 2 million seconds of integration time. ~100 million stars down to J<22, with ~40,000 measurements per star (~10% in bluer filter), N -1/2 = 1/200 ~20 billion photons detected for a J=20 star. Deepest IR image ever?

Extraordinarily rich dataset. Measure parallaxes to <10% and proper motions to <300 m/s (<0.3%) for 10 8 bulge and disk stars. – Larger than GAIA. Detect dark companions to disk and bulge stars. Find >10 5 transiting planets (Bennett & Rhie 2002). Detect 5000 KBOs down to 10km, with 1% uncertainties on the orbital parameters (Gould 2014). Exquisite characterization of the detector. ??

Microlensing Basics. Source Lens DlDl DsDs Image

Lens mass Relative Lens-Source Parallax Constant Angular Einstein Ring.

Rings vs. Images.

Microlensing Events. (t 0, u 0, t E ) tEtE t0t0 ~1/u 0 u0u0

Detecting Planets.

Basic Measurements. Primary Event: (t 0, u 0, t E ) Planetary Deviation: (t p, t c, ΔA)

t E, q, s All events: θEθE πEπE FlFl timescale, mass ratio, dimensionless projected separation Angular Einstein Ring Radius Microlens Parallax Lens Flux =f(M,D l ) combine any two m=qM, r perp = sθ E D l M l, D l

Angular Einstein Ring Radius. Need an angular ruler. – Finite size of source star ρ * =  * /  E –  * from source flux + color – Most planetary events. – Need measurements in two filters during the event. O SL rErE EE **

Lens Flux. Need to measure the lens flux. – Have to resolve out unrelated stars blended with lens and source. – Subtract source flux from sum of lens+source. – Remaining flux is due to the lens. – Need angular resolution better than ~0.3”. SpaceGround The field of microlensing event MACHO 96-BLG-5 (Bennett & Rhie 2002)

Microlens Parallax. Use the Earth’s orbit as a ruler. – Microlens parallax is a vector. – Direction of relative lens-source proper motion. – Measure deviations from a rectilinear, uniform trajectory. – Parallax asymmetry gives one component. – Precise lightcurves for most events give one component of parallax. (Gould & Horne 2013)

Other possible measurements. Additional parallax measurements. Directly measuring relative lens-source proper motion. Astrometric microlensing. Orbital motion.

Parallax, continued. Long timescale events. – Both components. Geosynchronous parallax (Gould 2013) – High magnification events. L2-Earth parallax (Yee 2013). – JWST+WFIRST Geo, or Earth+WFIRST L2 – Both components. – High-magnification events. – Requires alerts or dedicated surveys. (Gould 2013)

Directly measuring μ rel. For luminous lenses: Direct resolution of lens and source. – High μ rel events. – Precursor observations now! Image elongation. Color-dependent centroid shift. Useful for: Testing for companions to lens or source. Events where the finite source size is not measured.

Astrometric microlensing. Centroid shift of source. – Size is proportional to  E – Orientation is in the direction of μ rel and π E – Combined with parallax asymmetry, get complete solution. Can be used to measure masses of isolated remnants and brown dwarfs. Very small shift. – Worry about systematics. – Can be vetted using direct measurement of μ rel from precursor observations.

Summary. For planetary deviations with luminous lenses, will get (model dependent) masses. – Need two filters during the event. – Need high resolution. For planetary deviations with non-luminous lenses, will get partial information. – Need two filters during the event. – Need precise light curves. There are a variety of additional measurements we can make for a subset of events. – Additional information (orbits). – Redundancy to check solutions. – Strict control of systematics (photometry + astrometry). – ToO and/or Alerts. – Precursor observations.

Implications? Potentially very rich dataset, for microlensing and non-microlensing science, as well as for calibration of the detector. In order to extract the maximum amount of science from this dataset, we need to: – Think about what else can be done with this dataset. – Understand how and how well it can be used to calibrate the detector. – Figure out what additional measurements we might need to make now to maximally leverage this dataset for these purposes.

HST Precursor Survey. With HST imaging of (a subset of?) the WFIRST fields in several bluer filters: – Can measure metallicities, ages, distances, and foreground extinction for all the bulge and disk stars that will have WFIRST parallaxes and proper motions. – Can test proper motion and astrometric microlensing measurements by resolving the lenses and sources of future microlensing events. – Can identify and map out unusual stellar populations (blue stragglers, etc.) – Can identify the locations and colors of all of the stars in the microlensing fields with higher resolution and fidelity than WFIRST or Euclid.